This invention is a useful invention in the field of medicine. More detailedly, this invention relates to an industrially suitable process for preparation of a useful compound in the field of medicine, and novel preparation intermediates necessary for the preparation process and processes for preparation of the intermediates.
An indolopyrrolocarbazole derivative prepared by the preparation process of the invention and represented by the formula [I]: 
is a compound which has a carcinostatic activity and is now under clinical tests (Mitsuru Ohkubo et al., Bioorganic and Medicinal Chemistry Letters, volume 9, pages 3307-3312 (1999).
As to a process for preparation of the compound, there is a disclosure in WO95/30682.
The object of the invention lies in obviating undesirable points as an industrial preparation process from the process disclosed in WO95/30682. Namely, the object of the invention lies in deleting the steps shown below where highly physiologically active compounds are handled (Preparation steps of Compounds [b] and [c]), in the preparation process disclosed in WO95/30682. 
In the above, Ra represents a hydrogen atom, a lower alkyl group, a benzyloxymethyl group or an aralkyl group, and Rb, Rc, Rd, Re and Rf each represent a protective group of a hydroxyl group such as, for example, a benzyl group, a tolyl group, a p-methoxybenzyl group or a benzyloxymethyl group.
The present inventors have made sequential research into a process for preparation of the indolopyrrolocarbazole derivative [I], and as a result, they found the present preparation process of the indolopyrrolocarbazole derivative [I] which is excellent as an industrial process in the point that the step handling a highly physiologically active compound can be made to be only the final step, and completed the invention. Further, they also found that the respective preparation intermediates used in the preparation process of the indolopyrrolocarbazole derivative [I] of the invention are novel compounds.
Namely, the invention relates to the matters described in the following items (1) to (36).
(1) A process for preparation of an indolopyrrolocarbazole derivative represented by the formula [I] 
which comprises removing the protective groups of a compound represented by the general formula [II]: 
wherein R1, R2, R3, R4, R5 and R6 may be the same or different and each represent a protective group of a hydroxyl group, and R7 and R8 may be the same or different and each represent a hydrogen atom or a protective group of a hydroxyl group.
(2) The process according to item (1) wherein R1, R2, R3, R4, R5, R6, R7 and R8 are benzyl groups.
(3) The process according to item (1) wherein R1, R2, R3, R4, R5 and R6 are benzyl groups and R7 and R8 are hydrogen atoms.
(4) The process according to item (1) wherein the compound represented by the general formula [II] is obtained by reacting a compound represented by the general formula [IV]: 
wherein R1, R2, R3, R4, R5 and R6 may be the same or different and each represent a protective group of a hydroxyl group, with a hydrazinediol derivative acid addition salt represented by the general formula [III]: 
wherein X represents an acid molecule, and R7 and R8 may be the same or different and each represent a hydrogen atom or a protective group of a hydroxyl group, in the presence of an acid-capturing agent.
(5) The process according to item (4) wherein R1, R2, R3, R4, R5, R6, R7 and R8 are benzyl groups.
(6) The process according to item (4) wherein R1, R 2, R3, R4, R5 and R6 are benzyl groups and R7 and R8 are hydrogen atoms.
(7) The process according to item (4) wherein X is oxalic acid.
(8) The process according to item (4) wherein the compound represented by the general formula [IV] is obtained by treating a compound represented by the general formula [V]: 
wherein Y1 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a phenyl group, a benzyloxymethyl group or an aralkyl group, and R1, R2, R3, R4, R5 and R6 may be the same or different and each represent a protective group of a hydroxyl group, with a base in an inert solvent.
(9) The process according to item (8) wherein Y1 is a methyl group.
(10) The process according to item (8) wherein R1, R2, R3, R4, R5 and R6 are benzyl groups.
(11) A compound represented by the general formula [IV]: 
wherein R1, R2, R3, R4, R5 and R6 may be the same or different and each represent a protective group of a hydroxyl group.
(12) The compound according to item (11) wherein R1, R2, R3, R4, R5 and R6 are benzyl groups.
(13) A hydrazinediol derivative acid addition salt represented by the general formula [III]: 
wherein X represents an acid molecule, and R7 and R8 may be the same or different and each represent a hydrogen atom or a protective group of a hydroxyl group.
(14) The compound according to item (13) wherein R7 and R8 are benzyl groups.
(15) The compound according to item (13) wherein R7 and R8 are hydrogen atoms.
(16) The compound according to item (13) wherein X is oxalic acid.
(17) A hydrazinediol derivative represented by the general formula [III-a]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group.
(18) The compound according to item (17) wherein R7a and R8a are benzyl groups.
(19) A process for preparation of a hydrazinediol derivative acid addition salt represented by the general formula [III]: 
wherein R7a and R8a maybe the same or different and each represent a protective group of a hydroxyl group, and X represents an acid molecule,
which comprises reacting a hydrazinediol derivative represented by the general formula [III-a]: 
wherein R7a and R8a are as defined above, with an acid.
(20) The process according to item (19) wherein R7a and R8a are benzyl groups.
(21) The process according to item (19) wherein the hydrazinediol derivative represented by the general formula [III-a] is obtained by eliminating the protective group of the amino group of a hydrazinediol derivative represented by the general formula [III-b]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group.
(22) The process according to item (21) wherein R7a and R8a are benzyl groups and R9 is a t-butoxycarbonyl group.
(23) The process according to item (21) wherein the hydrazinediol derivative represented by the general formula [III-b] is obtained by reducing a hydrazone derivative represented by the general formula [III-c]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group, and R9 represents a protective group of an amino group.
(24) The process according to item (23) wherein R7a and R8a are benzyl groups and R9 is a t-butoxycarbonyl group.
(25) The process according to item (23) wherein the hydrazone derivative represented by the general formula [III-c] is obtained by reacting a dihydroxyacetone derivative represented by the general formula [III-e]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group,
with a hydrazine derivative represented by the general formula [III-d]: 
wherein R9 represents a protective group of an amino group, in a mixed solvent.
(26) The process according to item (25) wherein R7a and R8a are benzyl groups and R9 is a t-butoxycarbonyl group.
(27) The process according to item (25) wherein the dihydroxyacetone derivative represented by the general formula [III-e] is obtained by reacting a propanetriol derivative represented by the general formula [III-f]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group,
with a hypochlorite in an inert solvent in the presence of a catalyst and a buffer.
(28) The process according to item (27) wherein R7a and R8a are benzyl groups.
(29) A compound represented by the general formula [II]: 
wherein, R1, R2, R3, R4, R5 and R6 may be the same or different and each represent a protective group of a hydroxyl group, and R7 and R8 may be the same or different and each represent a hydrogen atom or a protective group of a hydroxyl group.
(30) The compound according to item (29) wherein R1, R2, R3, R4, R5, R6, R7 and R8 are benzyl groups.
(31) The compound according to item (29) wherein R1, R2, R3, R4, R5 and R6 are benzyl groups, and R7 and R8 are hydrogen atoms.
(32) A hydrazinediol derivative represented by the general formula [III-b]: 
wherein R7a and R8a each represent a protective group of a hydroxyl group and R9 represents a protective group of an amino group, or a salt thereof.
(33) The compound according to item (32) wherein R7a and R8a are benzyl groups and R9 is a t-butoxycarbonyl group.
(34) A hydrazone derivative represented by the general fomula [III-c]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group, and R9 represents a protective group of an amino group.
(35) The compound according to item (34) wherein R7a and R8a are benzyl groups and R9 is a t-butoxycarbonyl group.
(36) The process according to item (21) wherein the hydrazinediol derivative represented by the general formula [III-b] is obtained by reacting a propanediol derivative represented by the general formula [III-g]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group, and Y2 represents an eliminable group,
with a hydrazine derivative represented by the general formula [III-d]: 
wherein R9 represents a protective group of an amino group, in an inert solvent.
This invention is specifically and detailedly described below.
Description is made below on terminology used in the specification.
The xe2x80x9calkyl group having 1 to 4 carbon atomsxe2x80x9d means a straight-chain or branched alkyl group such as, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group or a t-butyl group, and among them preferred is a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group or the like, and further preferred is a methyl group, an ethyl group, a propyl group, an isopropyl group or a butyl group.
The xe2x80x9caralkyl groupxe2x80x9d means an aralkyl group having 7 to 12 carbon atoms such as, for example, a benzyl group, a 1-naphthylmethyl group or a 2-naphthylmethyl group, and preferred is a benzyl group.
The xe2x80x9cacid moleculexe2x80x9d means a protonic acid such as, for example, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, methylsulfonic acid, p-toluenesulfonic acid, oxalic acid or propionic acid, and preferred is oxalic acid.
The xe2x80x9ca protective group of a hydroxyl groupxe2x80x9d includes a protective group of a hydroxyl group such as, for example, a benzyl group, a p-nitobenzyl group, a p-methoxybenzyl group or a benzyloxymethyl group, and preferred is a benzyl group.
The xe2x80x9ca protective group of an amino groupxe2x80x9d includes a protective group of a hydroxyl group such as, for example, a methoxycarbonyl group, an ethoxycarbonyl group, a t-butoxycarbonyl group or a benzyloxycarbonyl group, and preferred is a t-butoxycarbonyl group.
The first step of the preparation process of the invention, namely, the step comprising treating a compound represented by the general formula [V]: 
wherein Y1 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a phenyl group, a benzyloxymethyl group or an aralkyl group, and R1, R2, R3, R4, R5 and R6 may be the same or different and each represent a protective group of a hydroxyl group, and R7 and R8 may be the same or different and each represent a hydrogen atom or a protective group of a hydroxyl group,
with a base in an inert solvent to prepare a compound represented by the general formula [IV]: 
wherein R1, R2, R3, R4, R5 and R6 are as defined above, is usually carried out in an inert solvent having no bad influence on the reaction, using 50 to 100 moles, preferably 50 to 70 moles of a base per 1 mole of the compound represented by the general formula [V].
As the inert solvent, there can, for example, be mentioned an alcohol such as methanol, ethanol, isopropanol or t-butanol; dimethylsulfoxide; or a mixed solvent thereof, etc., and particularly preferred is methanol, ethanol, isopropanol or the like.
As the base, there can be mentioned a base such as, for example, sodium hydroxide, potassium hydroxide, potassium methoxide, sodium methoxide, sodium t-butoxide or potassium t-butoxide, etc., and particularly preferred is sodium hydroxide, potassium hydroxide, sodium methoxide or the like.
The reaction temperature is, usually, room temperature to about 60xc2x0 C., preferably 30xc2x0 C. to 50xc2x0 C., and the reaction time is, usually, 1 hour to 1 day, preferably, 3 hours to 10 hours.
The compound represented by the general formula [V] as the raw material used in the above step can be prepared or obtained, for example, by the process described in WO95/30682 or the like.
The step comprising reacting the compound [IV] obtained by the above step with a hydrazinediol derivative acid addition salt represented by the general formula [III]: 
wherein X represents an acid molecule, and R7 and R8 may be the same or different and each represent a hydrogen atom or a protective group of a hydroxyl group,
in the presence of an acid-capturing agent to prepare a compound represented by the general formula [II]: 
wherein R1, R2, R3, R4, R5, R6, R7 and R8 are as defined above, is usually carried out in an inert solvent having no bad influence on the reaction in the presence of an acid-capturing agent, using equimolar to 1.5 moles, preferably 1.2 to 1.3 moles of the compound of the general formula [III] per 1 mole of the compound of the general formula [IV].
As the inert solvent, there can, for example, be mentioned N,N-dimethylformamide, N,N-dimethylactamide, tetrahydrofuran, dimethylsulfoxide, N-methylpyrrolidone or a mixed solvent thereof, etc., and particularly preferred is N,N-dimethylformamide, N,N-dimethylactamide, N-methylpyrrolidone or the like.
The reaction temperature is, usually, room temperature to about 60xc2x0 C., preferably about 30xc2x0 C. to 50xc2x0 C., and the reaction time is, usually, 1 hour to 1 day, preferably, 1 hour to 3 hours.
As the acid-capturing agent, there can, for example, be mentioned triethylamine or 4-dimethylaminopyridine, and preferred is triethylamine.
As to the step comprising removing the protective groups of the compound [II] obtained in the above step to prepare an indolopyrrolocarbazole derivative represented by the formula [I]: 
, when this reaction is carried out by catalytic reduction, the catalyst includes, for example, palladium-carbon catalyst, Raney nickel catalyst or the like.
The hydrogen pressure in the catalytic reduction is, usually, preferably normal pressure to 2 atoms, and the use amount of the catalyst is usually {fraction (1/100)} to 1 times, preferably {fraction (1/100)} to {fraction (1/10)} times the weight 1 of the compound represented by the general formula [II] as the raw material.
As the reaction solvent, there can, for example, be mentioned a mixed solvent of an alcoholic solvent such as methanol, ethanol or butanol with tetrahydrofuran, and preferred is a mixed solvent of methanol/tetrahydrofuran (50/50).
The reaction temperature is, usually, about xe2x88x9230xc2x0 C. to 60xc2x0 C., preferably about 0xc2x0 C. to 50xc2x0 C., and the reaction time is, usually, instantaneous to 7 days, preferably instantaneous to 24 hours.
Each of compounds obtained in the above preparation steps can be purified or isolated by using methods known per se, namely commonly used separation or purification methods such as, for example, column chromatography, liquid chromatography or thin layer chromatography each using silica gel or an adsorption resin, solvent extraction and recrystallization or reprecipitation, according to necessity solely or in an appropriate combination of two or more.
Description is made below on respective steps for preparation of a hydrazinediol derivative acid addition salt represented by the general formula [III]: 
wherein X represents an acid molecule, and R7 and R8 may be the same or different and each represent a hydrogen atom or a protective group of a hydroxyl group,
which is one of the raw material compounds in the preparation process of the invention.
The step of preparing a dihydroxyacetone derivative represented by the general formula [III-e]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group, by reacting a propanetriol derivative represented by the general formula [III-f]: 
Wherein R7a and R8a are as defined above, with a hypochlorite in an inert solvent in the presence of a buffer can be carried out by adding the catalyst and the buffer to the inert solvent, adding the hypochlorite at xe2x88x9230xc2x0 C. to 50xc2x0 C., preferably xe2x88x9210xc2x0 C. to 10xc2x0 C. over a period of 1 hour to 3 hours, preferably 1.5 hours to 2 hours, and making reaction at the same temperature for 1 hour to 3 hours, preferably 1.5 hours to 2 hours.
It is possible to use, per 1 mole of the propanetriol derivative represented by the general formula [III-f], 0.005 mole to 1.0 mole, preferably 0.05 mole to 0.15 mole of the catalyst, 0.5 mole to 2.0 moles, preferably 1.0 mole to 1.5 moles of the buffer and 0.5 mole to 2.0 moles, preferably 1.0 mole to 1.5 moles of the hypochlorite.
As the inert solvent used in the step, there can, for example, be mentioned dimethylsulfoxide, dimethylformamide, dimethyl-acetamide, acetonitrile, propionitrile, toluene, xylene or benzene, etc., and preferred is acetonitrile or propionitrile.
As the catalyst used in the step, there can be mentioned 
The catalysts are on the market or known compounds described in literatures, and are available.
As the buffer used in the step, any buffer can be used as long as change of the pH of the reaction mixture by addition of the hypochlorite can be inhibited, but there can be mentioned a 0.5% to saturated aqueous sodium bicarbonate solution, a phosphate buffer solution or the like.
As the hypochlorite used in the step, there can, for example, be used sodium hypochlorite, potassium hypochlorite, calcium hypochlorite or the like.
The raw material used in the step (the compound represented by the general formula [III-f]) can be prepared according to a known process (Canadian Journal of Chemistry, vol. 62, page 241 (1984)) or a commercial product can also be utilized.
As to this step, in the case of a known process (Tetrahedron, vol. 55, page 739 (1999)), it is carried out to adjust a sodium hypochlorite solution, prepared separately from the reaction solution, with sodium bicarbonate to pH 9.5 and, immediately thereafter, add the mixture to the reaction solution. In this case, there were a drawback that since chlorine gas is formed at the pH adjustment, the process is not proper as an industrial preparation process and a drawback that since it is difficult to add the hypochlorite with accuracy, impurities are formed by excessive oxidation. In this invention, by previously adding the buffer to the reaction solution and gradually adding the hypochlorite, the drawbacks of the known process can be obviated and the yield of the step can be increased.
The step of preparing a hydrazone derivative represented by the general formula [III-c]: 
wherein R7a and R8a are as defined above, and R9 represents a protective group of an amino group,
by reacting the thus obtained dihydroxyacetone derivative represented by the general formula [III-e] with a hydrazine derivative represented by the general formula [III-d]: 
wherein R9 is as defined above, in a mixed solvent can be carried out by making reaction in the mixed solvent at 70xc2x0 C. to 80xc2x0 C., preferably 70xc2x0 C. to 75xc2x0 C. for 1 hour to 3 hours, preferably 1 hour to 1.5 hours.
The hydrazine derivative represented by the general formula [III-d] can be used in a ratio of 1.0 mole to 8.0 moles, preferably 1.1 moles to 1.5 moles per 1 mole of the dihydroxyacetone derivative represented by the general formula [III-e].
The mixed solvent used in the step is a mixed solvent obtained by mixing benzene, toluene, ethanol, isopropanol, acetonitrile or the like with an aliphatic hydrocarbon such as hexane or heptane in a ratio of 50:1 to 10:1 (volume ratio), preferably 30:1 to 20:1 (volume ratio).
In a known process (Journal of Organic Chemistry, vol.46, page 5413 (1981)), this step is carried out under a reaction condition such as reflux for 20 minutes in a single solvent (hexane). But, when the step is carried out under such a condition, there arise such problems that the purity of the hydrazone derivative prepared is low, and that the by-products formed remain in the final product.
According to the present invention, the problems of the known process can be obviated by, after the reaction at 70xc2x0 C. to 80xc2x0 C. for 1 hour to 3 hours in the mixed solvent, crystallizing the hydrazone derivative represented by the general formula [III-c] at 60xc2x0 C. and gradually lowering the temperature of the reaction mixture to room temperature.
The step of preparing a hydrazinediol derivative represented by the general formula [III-b]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group, and R9 represents a protective group of an amino group,
by reducing a hydrazone derivative represented by the general formula [III-c]: 
wherein R7a, R8a and R9 are as defined above, can be carried out by reacting 2- to 5-fold moles of a reducing agent at 0xc2x0 C. to 80xc2x0 C., preferably 0xc2x0 C. to 70xc2x0 C. for 30 minutes to 48 hours, preferably 1 hour to 41 hours in the presence or absence of an inert solvent.
As the inert solvent used in the step, there can be mentioned an organic solvent such as, for example, heptane, hexane, methanol, ethanol or tetrahydrofuran, and preferred is tetrahydrofuran, ethanol or in the absence thereof.
As the reducing agent used in the step, there can be mentioned a reducing agent such as, for example, BH3-tetrahydrofuran complex, NaBH4, NaHB(OAc)3, NaH3BCN, diborane, BH3-dimethylsulfide, Raney nickel, diisobutylaluminum hydride (DIBAL), Zn(BH4)2, LiBH4, Ptxe2x80x94S/C or LiAlH4, and preferred is BH3-tetrahydrofuran complex or NaBH4.
When the reducing agent is a boron compound, for accelerating the generation of BH3 in the reaction system, it is possible to add 0.5 to 1.0 mole of, for example, BF3, BCl3, sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid, hydrochloric acid, aluminum chloride, zinc chloride, dimethyl sulfate, diethyl sulfate, methyl iodide or the like per 1.0 mole of the reducing agent.
The step of eliminating the protective group of the amino group (R9) of the hydrazinediol derivative represented by the general formula [III-b]: 
wherein R7a, R8a and R9 are as defined above, can be carried out by making 2 to 20 equivalents of an inorganic acid act in a solvent such as, for example, tetrahydrofuran at 50xc2x0 C. to 100xc2x0 C. for 3 hours to 24 hours.
As the inorganic acid, there can, for example, be mentioned hydrochloric acid, sulfuric acid or nitric acid, and preferred is 6-normal hydrochloric acid.
The step of preparing a hydrazinediol derivative acid addition salt represented by the general formula [IIIxe2x80x2]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group, and X represents an acid molecule,
by reacting the thus obtained hydrazinediol derivative represented by the general formula [III-a]: 
wherein R7a and R8a are as defined above, with an acid can be carried out by reacting 0.5 equivalent to 2 equivalents of an acid in an inert solvent such as, for example, methyl t-butyl ether or a mixed solvent of methyl t-butyl ether with methanol at room temperature to 40xc2x0 C. for 30 minutes to 2 hours.
As the acid used in the step, there can, for example, be mentioned a protonic acid such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, methylsulfonic acid, p-toluenesulfonic acid, oxalic acid or propionic acid, and preferred is oxalic acid.
The step of preparing a hydrazinediol derivative represented by the general formula [III-b]: 
wherein R7a and R8a may be the same or different and each represent a protective group of a hydroxyl group, and R9 represents a protective group of an amino acid,
by reacting a propanediol derivative represented by the general formula [III-g]: 
wherein R7a and R8a are as defined above, and Y2 represents an eliminable group,
with a hydrazine derivative represented by the general formula [III-d]: 
wherein R9 is as defined above, in an inert solvent can be carried out by carrying out the reaction in an inert solvent such as, for example, N,N-dimethylformamide, tetrahydrofuran, N-methylpyrrolidone or dimethylsulfoxide at 80xc2x0 C. to 150xc2x0 C., preferably 100xc2x0 C. to 120xc2x0 C. for 50 hours to 100 hours, preferably 70 hours to 80 hours.
The use amount of the hydrazine derivative represented by the general formula [III-d] is 1 equivalent to 20 equivalents, preferably 1.5 equivalents to 3 equivalents based on the propanetriol derivative represented by the general formula [III-g]
The eliminable group represented by Y2 means an eliminable group such as, for example, a methylsulfonyloxy group, a chloromethylsulfonyloxy group, a p-toluenesulfonyloxy group, a trifluoromethylsulfonyloxy group or a p-nitrobenzene-sulfonyloxy group.
The propanetriol derivative represented by the general formula [III-g] can be obtained by a process described in a literature such as, for example, Journal of the Chemical Society Perkin Transaction-I, page 2757 (1988) or a process applying the former process similarly.
In the hydrazine derivative acid addition salt represented by the general formula [III]: 
wherein X represents an acid molecule, and R7 and R8 each represent a hydrogen atom or a protective group of a hydroxyl group,
as one of the raw material compounds in the preparation process of the invention, the compound wherein R7 and R8 are hydrogen atoms can be prepared by preparing a compound represented by the formula [VIII]: 
according to the preparation process disclosed in WO95/30682 and carrying out the same treatment as in the aforementioned step where a hydrazinediol derivative represented by the general formula [III-a] is converted to its acid addition salt.
Compounds obtained in the above respective preparation steps can be purified or isolated by methods known per se, namely by using commonly used separation or purification methods such as, for example, column chromatography, liquid chromatography or thin layer chromatography using silica gel, an adsorption resin or the like, solvent extraction, and recrystallization or reprecipitation, alone or in an appropriate combination thereof according to necessity.
Description is made below on usefulness of the preparation process of the invention as an industrial preparation process.
The compound represented by the formula [VIII]: 
, which is a known compound (disclosed in WO95/30682), is an oily substance and low in stability, and from reasons as above, must be stored in an solvent at low temperatures, whereas the hydrazinediol derivative acid addition salt represented by the general formula [III]: 
wherein X represents an acid molecule, and R7 and R8 each represent a hydrogen atom or a protective group of a hydroxyl group, which is one of the preparation raw materials of the invention, is in the form of crystals, and thus is easy to isolate and has high stability, and therefore, possesses more suitable properties and state than the known substance for industrial preparation.
And as apparent from the experimental results of Table 1, the preparation intermediates according to the preparation process of the invention are far lower in inhibitory activity on topoisomerase I than the intermediates in the known process (the preparation process disclosed in WO95/30682), and therefore can be prepared using usual facilities and it is possible to reduce a danger that workers relating to the preparation steps are exposed to highly active compounds. Therefore, the preparation process of the invention can be said to be an industrial preparation process excellent in the aspect of the preparation facilities and the aspect of safety of the workers, compared with the known process.
Topoisomerase I-inhibiting activity was assayed by the method described in Yoshinari, T et al., Cancer Research, vol. 55, page 1310 (1995).
In the table, EC50 means the concentration of a compound needed to inhibit topoisomerase I activity by 50%.